The heart is a four-chambered pump that moves blood efficiently through the vascular system. Blood enters the heart through the vena cava and flows into the right atrium. From the right atrium, blood flows through the tricuspid valve and into the right ventricle, which then contracts and forces blood through the pulmonic valve and into the lungs. Oxygenated blood returns from the lungs and enters the heart through the left atrium and passes through the bicuspid mitral valve into the left ventricle. The left ventricle contracts and pumps blood through the aortic valve into the aorta and to the vascular system.
The mitral valve consists of two leaflets (anterior and posterior) attached to a fibrous ring or annulus. In a healthy heart, the mitral valve leaflets overlap during contraction of the left ventricle and prevent blood from flowing back into the left atrium. However, due to various cardiac diseases, the mitral valve annulus may become distended, causing the leaflets to remain partially open during ventricular contraction and thus allowing regurgitation of blood into the left atrium. This results in reduced ejection volume from the left ventricle, causing the left ventricle to compensate with a larger stroke volume. The increased workload eventually results in dilation and hypertrophy of the left ventricle, further enlarging and distorting the shape of the mitral valve. If left untreated, the condition may result in cardiac insufficiency, ventricular failure, and death.
It is common medical practice to treat mitral valve regurgitation by valve replacement or repair. Valve replacement involves an open-heart surgical procedure in which the patient's mitral valve is removed and replaced with an artificial valve. This is a complex, invasive surgical procedure with the potential for many complications and a long recovery period.
Mitral valve repair includes a variety of procedures to repair or reshape the leaflets to improve closure of the valve during ventricular contraction. If the mitral valve annulus has become distended, a common repair procedure involves implanting an annuloplasty ring on the mitral valve annulus. The annuloplasty ring generally has a smaller diameter than the annulus, and when sutured to the annulus, the annuloplasty ring draws the annulus into a smaller configuration, bringing the mitral valve leaflets closer together and providing improved closure during ventricular contraction.
Annuloplasty rings may be rigid, flexible, or have both rigid and flexible segments. Rigid annuloplasty rings have the disadvantage of causing the mitral valve annulus to be rigid and unable to flex in response to the contractions of the ventricle, thus inhibiting the normal movement of the mitral valve that is required for it to function optimally. Flexible annuloplasty rings are frequently made of Dacron® fabric and must be sewn to the annular ring with a line of sutures. This eventually leads to scar tissue formation and loss of flexibility and function of the mitral valve. Similarly, combination rings must generally be sutured in place and also cause scar tissue formation and loss of mitral valve flexibility and function.
Annuloplasty rings have been developed that do not require suturing. U.S. Pat. No. 6,565,603 discloses a combination rigid and flexible annuloplasty ring that is inserted into the fat pad of the atrioventricular groove, which surrounds the mitral valve annulus. Although this device avoids the need for sutures, it must be placed within the atrioventricular groove with great care to prevent tissue damage to the heart.
U.S. Pat. No. 6,569,198 discloses a flexible annuloplasty ring designed to be inserted into the coronary sinus, which is located adjacent to and partially surrounds the mitral annulus. The prosthesis is shortened lengthwise within the coronary sinus to reduce the size of the mitral annulus. However, the coronary sinus in a particular individual may not wrap around the heart far enough to allow effective encircling of the mitral valve, making this treatment ineffective.
U.S. Pat. No. 6,210,432 discloses a flexible elongated device that is inserted into the coronary sinus and adapts to the shape of the coronary sinus. The device then undergoes a change that causes it to assume a reduced radius of curvature and, as a result, causes the radius of curvature of the coronary sinus and the circumference of the mitral annulus to be reduced. While likely to be effective for modest changes in the size or shape of the mitral annulus, this device may cause significant tissue compression in patients requiring a larger change in the configuration of the mitral annulus.
U.S. patent application Publication No. 2003/0105520 discloses a flexible elongated device that is inserted into the coronary sinus and anchored at each end by a self-expanding, toggle bolt-like anchor that expands and engages the inner wall of the coronary sinus. Application WO02/076284 discloses a similar flexible elongated device that is inserted into the coronary sinus. This device is anchored at the distal end by puncturing the wall of the coronary sinus, crossing the intervening cardiac tissue, and deploying the anchor against the exterior of the heart in the pericardial space. The proximal end of the elongated member is anchored against the coronary ostium, which connects the right atrium and the coronary sinus. Once anchored at each end, the length of either of the elongated devices may be adjusted to reduce the curvature of the coronary sinus and thereby change the configuration of the mitral annulus. Due to the nature of the anchors, both of these devices may cause significant damage to the coronary sinus and surrounding cardiac tissue. Also, leaving a device in the coronary sinus may result in formation and breaking off of a thrombus that may pass into the right atrium, right ventricle, and ultimately the lungs, causing a pulmonary embolism. Another disadvantage is that the coronary sinus is typically used for placement of a pacing lead, which may be precluded with the placement of the prosthesis in the coronary sinus.
U.S. Pat. No. 6,616,684 discloses a splint assembly that is positioned transverse the left ventricle to treat mitral valve leakage. In one embodiment, the assembly is delivered through the right ventricle. One end of the assembly is anchored outside the heart, resting against the outside wall of the left ventricle, while the other end is anchored within the right ventricle, against the septal wall. The heart-engaging portions of the assembly, i.e., the anchors, are essentially flat and lie snugly against their respective walls. The length of the splint assembly is either preset or is adjusted to draw the two walls of the chamber toward each other.
The splint assembly may be delivered endovascularly, which offers distinct advantages over open surgery methods. However, the endovascular delivery technique is complicated, involving multiple delivery steps and devices, and requiring that special care be taken to avoid damage to the pericardium and lungs. First, a needle or guidewire is delivered into the right ventricle, advanced through the septal wall, and anchored to the outer or free wall of the left ventricle using barbs or threads that are rotated into the tissue of the free wall. Visualization is required to ensure the needle does not cause damage beyond the free wall. A delivery catheter is then advanced over the needle, piercing both the septal wall and the free wall of the ventricle. The catheter is anchored to the free wall with balloons inflated on either side of the wall. A tension member is then pushed through the delivery catheter such that a distal anchor is positioned outside the heart. During the catheter anchoring and distal anchor positioning steps, care must be taken to guard against damaging the pericardium or lungs, and insufflation of the space between the myocardium and the pericardial sac may be desirable. A securing band is advanced over the tension member to expand the distal anchor and/or maintain it in an expanded configuration. The catheter is withdrawn, and a second (proximal) anchor is advanced over the tension member using a deployment tool and positioned within the right ventricle against the septal wall. A tightening device then holds the second anchor in a position so as to alter the shape of the left ventricle. Excess length of the tension member is thermally severed prior to removal, again posing some risk to tissue in and around the heart.
Therefore, it would be desirable to provide a system and method for treating mitral valve regurgitation that overcome the aforementioned and other disadvantages.